"They like hard ice cream."
Translation:De liker hard iskrem.
I wouldn't call anything that myself, but we have soft ice (either called just that or softis), the half frozen kind they make fresh from a machine into a biscuit cone and you eat it right away. And then you have your standard bucket of frozen something you buy at the supermarket to take home with you. That one is hard. (And from the sweet tooth perspective there's always gelato, and frozen yoghurt, and sorbets, and the frozen juice/limonade saftis but they mostly come on a stick or in a plastic tube)
In Norway you would be asked if you wanted ice. "Is." Har du lyst på is?
In people's homes most often it is the hard kind of ice cream you can buy in a box at the supermarket. Or the smaller one-serving kind (families with small children often has some, bought from "is-bilen"), which can be both cream and juice. But your host usually will quickly specify what sort is in question.